body {
  margin: 0px;
}

.flex-box {
  display: flex;
}

.border-box {
  border: 1px solid #ff0000;
  padding: 1rem;
}

.border-box01 {
  border: 5px solid #0000ff;
}

.box01 {
  flex-direction: column;
  height: 300px;
  justify-content: space-between;
}

.box02 {
  flex-direction: column;
  height: 300px;
}

.box02 > div:nth-child(2) {
  flex: 1;
}
.box02 > div:nth-child(3) {
  flex: 3;
}

.fixed-box {
  position: fixed;
  top: 0px;
  left: 0px;
  width: 100%;
  text-align: center;
  background-color: rgba(0, 0, 0, 0.5);
}
